Multi-wall bag

ABSTRACT

A coated paper and a multi-wall bag formed from the coated paper is provided. The coated paper uses a kraft stock paper having a polyethylene layer applied to one surface. On top of the polyethylene layer, a biaxially oriented thermoplastic layer is provided such as polypropylene or polyester. Additionally, the biaxially oriented thermoplastic layer may include a foil or metal layer. The coated paper is resistant to water, greases, fats, and oils and provides an improved printing surface for graphics and enhances the strength of bag structures comprising the coated paper.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisionalapplication having application serial No. 60/429,004 filed Nov. 25,2002, and which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] This invention is directed towards a multi-wall bag having atubular form comprising a plurality of overlapping, paper-containingplies of flexibly shaped material. Such bags are commonly used inpackaging of pet food.

BACKGROUND OF THE INVENTION

[0003] This invention relates to stand-up pouches and multi-wall bagsfor use in packaging granulated or powdered products such as animalfeed, chemicals, powdered milk, and other pourable types of products.Bags and pouches within this industry are frequently referred to asself-opening style (SOS) bags, pinched-bottom or open-mouthed bags, andvalve sacks which are hereinafter collectively referred to as multi-wallbags. A multi-wall bag frequently includes a tear open tab located atleast partially inside the bag and which is folded with the pinchedclosure between the walls of the bag.

[0004] One form of a multi-wall bag may be seen in reference to U.S.Pat. No. 3,687,356 assigned to St. Regis Paper Company and whichdescribes single-wall and multi-ply wall gusseted type bags. Multi-wallbags of this basic construction have been widely used for the packagingof animal feed, particularly dog and cat food.

[0005] Recently, the exterior ply of multi-wall bags used within the petfood packaging industry were treated with fluorocarbons such as ScotchGuard® brand FC807 (3M) protectants designed to provide grease/oilresistance to the exterior surface of the outermost bag ply. Thegrease/oil barrier was achieved by adding the fluorocarbon to the pulpprior to making the paper. Additionally, clay-coated papers hadadditional fluorocarbon added to the clay slurry prior to coating thepaper. Such treatments prevented grease and oil from sticking to theconstituent paper fibers. Such chemical treatment has been adequate toprovide grease/oil resistance to the bag's exterior surface whilepermitting the application of graphics and printing using conventionalprinting techniques.

[0006] Useful background information with respect to multi-wall bagcontainers may be found in the publication entitled, Reference Guide ForThe Paper Shipping Sack Industry, Copyright 1991, published by the PaperShipping Sack Manufacturer's Association, Inc., of Tarrytown, N.Y., a51-page guide which is incorporated herein by reference. The referenceguide discusses paper finishes and treatments including use offluoro-chemical agents to make paper resistant to oil and grease. Whilefluorocarbon coating of papers used to construct multi-wall bags hasproven adequate within the industry, there remains room for improvementand variation within the art.

SUMMARY OF THE INVENTION

[0007] It is one aspect of one of the present embodiments of theinvention to provide a paper layer suitable for use as the outermost plyof a single-ply or a multi-wall bag having improved resistanceproperties to grease, fat, and oils of animal or plant derivation andwhich exhibits excellent graphic printing capabilities.

[0008] It is yet another aspect of at least one of the presentembodiments of the invention to provide a paper layer suitable for useas an outermost ply of a single-ply or a multi-wall bag having an outerply layer of a coated paper which provides improved resistance to water,has improved graphic printing capabilities, and increased tearresistance and strength properties compared to similar bags having anuncoated outer ply.

[0009] It is yet another aspect of at least one of the presentembodiments of the invention to provide a paper layer suitable for useas a ply layer of a multi-wall bag in which the paper layer provides forlow water vapor transmission rates (WVTR).

[0010] It is yet another aspect of at least one of the presentembodiments of the invention to provide a multi-wall bag in which theouter ply layer comprises a natural kraft or bleached paper having afilm layer of a biaxially oriented thermoplastic material such aspolypropylene or polyester positioned as an outermost layer. An extrudedthermoplastic layer, and/or a glue layer such as a conventional tieresin, polyurethane adhesive, or polyester adhesive, may be presentbetween the paper and the film layer.

[0011] It is another aspect of at least one of the present embodimentsof the invention to provide for a multi-wall bag construction having anoutermost ply of a coated paper. The outer ply of coated paper resultsin an overall greater bag strength and brings about noted improvementsin graphics, printing capabilities, and water vapor transmission rates,and permits bag dimensions of face width, tube length, and gusset widthto be varied without having to change the composition or characteristicsof the various ply layers which make up the bag. The added strengthprovided by the exterior coated paper substrate enhances the strength ofthe resulting bags such that standard variations in useful bagdimensions all have adequate strength for conventional bag contents suchas pet food, cat litter, bird seed, and similar materials.

[0012] It is yet another aspect of at least one of the presentembodiments of the invention to provide a coated paper layer suitablefor use within a stand-up pouch container or a multi-wall bag in which acoated paper provides the outermost ply, the coated paper having anextruded structural layer of polyethylene to which a barrier film layeris bonded. The barrier film layer provides moisture resistance to theouter ply along with increased grease, fat, and oil resistance. Thecoated paper further provides an improved printing surface as comparedto an untreated paper. Additionally, the coated paper constituent layersprovide a structural reinforcement to the base paper such that when thematerial is used as an outer ply for a multi-wall bag, the resulting bagstrength is increased in comparison to an outer ply lacking the film andextruded layers.

[0013] It is yet another aspect of at least one of the presentembodiments of the invention to provide for a three-ply multi-wall bagin which the outermost ply layer defines a coated paper layer comprisingan outer layer of a biaxially oriented polyester, polypropylene, orother oriented thermoplastic film layer. The resulting ply of coatedpaper permits a 3-ply bag strength which is equivalent to or greaterthan that of a 4-ply multi-wall bag using similar ply layers with anuncoated outer ply.

[0014] These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A fully and enabling disclosure of the present invention,including the best mode thereof, to one of ordinary skill in the art isset forth more particularly in the remainder of the specification,including reference to the accompanying drawings.

[0016]FIG. 1 is a perspective view of a single-ply, pinch-bottom bagconstruction in accordance with the invention.

[0017]FIG. 2 is a perspective view of an alternative embodiment of theinvention showing a multi-wall 3-ply bag construction in which the bagplies are successively stepped along the open end of the bag.

[0018]FIG. 3 is a cross-section taken along line 3-3 of FIG. 1 providingdetails of a coated paper construction of one embodiment of the presentinvention.

[0019]FIG. 4 is a cross-section similar to FIG. 3 setting forth analternative embodiment of a coated paper construction according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] Reference will now be made in detail to the embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncover such modifications and variations as come within the scope of theappended claims and their equivalents. Other objects, features, andaspects of the present invention are disclosed in the following detaileddescription. It is to be understood by one of ordinary skill in the artthat the present discussion is a description of exemplary embodimentsonly and is not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstructions.

[0021] In describing the various figures herein, the same referencenumbers are used throughout to describe the same material, apparatus orprocess pathway. To avoid redundancy, detailed descriptions of much ofthe apparatus once described in relation to a figure is not repeated inthe descriptions of subsequent figures, although such apparatus orprocess is labeled with the same reference numbers.

[0022] As used herein, the term “coated paper” refers to a paper havinga surface to which is adhered a biaxially oriented polyester orpolypropylene film layer. One or more intervening layers of an extrudedmaterial or adhesive may also be present.

[0023] As seen in reference to FIGS. 1 and 2, an exemplary, non-limitingembodiment of the present invention is directed to a stand-up pouch ormulti-wall bag having a pinched closure at one end. As seen in referenceto FIG. 1, the bag 10 defines at least one pinch-closable end and isformed from a ply of paper 20 which is folded to form a pinch closure.As seen in reference to FIG. 1, bag 10 may be formed from a single paperply 20. The bag has a front wall 12 and an oppositely disposed rear wall14, rear wall 14 extending above the front surface 12 at one end of thetube when the bag is in its assembled condition as illustrated. As seenin FIG. 1, the bag 10 defines a series of forward fold lines 22, 24, 26,and 28. Bag 10 further defines a pair of oppositely spaced gussets 32and 34 which are positioned between the respective front and rear wallsof bag walls 12 and 14.

[0024] In reference to FIG. 2, a multi-ply bag embodiment is referencedhaving a rear wall 14 that comprises a plurality of three pliesincluding an outer ply 50 of a coated paper as described herein, asecond ply 52, and an innermost ply layer 54. Ply layers 52 and 54 maybe formed of natural kraft paper, converter kraft, or other conventionalpaper stock. The construction of single-wall and multi-wall gussetedtype bags is well known in the art as may be found in reference to U.S.Pat. Nos. 3,687,356 and 6,599,016 which are incorporated herein byreference.

[0025] Exemplary bags seen in FIGS. 1 and 2 may be constructed from acoated paper in which the single ply or outermost ply comprises a coatedpaper having an exterior surface of a biaxially oriented film layer. Asbest seen in reference to FIG. 3, one embodiment of a coated paper 20 isprovided in which paper 20 comprises an innermost paper substrate layer40. Paper substrate layer 40 may be in the form of a natural kraft,converter kraft, bleached paper, or extensible kraft paper. Conventionalpaper weights for multi-wall bags used in the pet food industry usekraft paper for inner ply layers corresponding to a 40 to 60 poundweight paper. Along an exterior surface of the coated paper 20, a 5 to15 pound layer (per 3000 sq. ft. of paper stock) of a polyethylene 42 isextrusion coated onto the paper. The polyethylene extruded layer 42provides a smooth surface to the coated paper while providing a bondablesurface for applying a subsequent film layer. Useful polyethylenes forlayer 42 include low density polyethylene (LDPE), linear low densitypolyethylene (LLDPE), polyethylene-based adhesive tie layers,polyethylene terepthalate (PET), as well as other polymers asconventionally used to laminate paper or paperboard substrates.Following application of the polyethylene layer 42, a biaxially orientedthermoplastic material 44 such as polypropylene or polyester film isapplied. When polyester film is used, a useful thickness of thebiaxially oriented film layer is about 48 gauge, although a range ofabout 30 gauge to about 98 gauge is believed useful. In the case ofbiaxially oriented polypropylene, a film thickness of about 55 gauge hasbeen found useful, although it is believed that a range of about 40 toabout 100 gauge is also useful. Applying a biaxially oriented polyesteror polypropylene film to a paper or laminated paper substrate may becarried out using conventional techniques well known within the art.

[0026] In accordance with the present invention, it has been found thatpolypropylene biaxially oriented films having a melting point of between325° to 330° F. prove useful. In addition, it has been found that havingan acrylic coating applied to the exterior surface of the film, i.e.,print ink receiving surface, improves the film's surface receptivity toinks and hot melts. Suitable polypropylene films, including films havingacrylic coatings are commercially available from AET Films, Inc. (NewCastle, Del.) and ViFan, a division of Vibac (Morristown, Tenn.).Further, it has been noted that selection of a smooth finished kraftpaper such as machine glazed paper available from Longview Fibre Company(Longview, Wash.), may reduce by up to 50 percent the amount of thepolyethylene extrusion coating required to achieve a smooth surface forapplying the subsequent film layer 44.

[0027] As seen in reference to FIG. 4, an alternative embodiment of thepresent invention makes use of a paper layer 40 with an extrudedpolyethylene layer 42 similar to that described above in reference toFIG. 3. The biaxially oriented thermoplastic layer may additionallyinclude a foil or metal layer 48. By way of example, an aluminum foillayer may have a thickness of about 1 to 2 angstroms with an opticaldensity (OD) ranging from about 2.0 to about 3.5. On top of the foillayer 48 is the biaxially oriented thermoplastic layer 44 ofpolypropylene or polyester. Preferably, metal layer 48 and thethermoplastic film layer 44 may be applied in a single step using avacuum metallized oriented polypropylene sheet. Suitable metallizedoriented polypropylene film is available from AET Films, Inc. (NewCastle, Del.) and ViFan (Morristown, Tenn.).

[0028] In paper layer 40, seen in reference to FIGS. 3 and 4, thepolyethylene layer 42 provides a smooth, outer surface to the paperlayer 40. The smooth surface provided by layer 42 facilitates thesubsequent application of the polypropylene or polyester film 44 andwhich may include optional foil layer 48. As a result, film 44 providesa smooth, even exterior surface which facilitates subsequent printing ofbag graphics onto film layer 44 using, for example, conventional flexoprinting or gravure printing techniques. In the described embodiments,there is no need for an overprint varnish or separate oil/greaseresistant coating to be applied following printing.

[0029] In accordance with the present invention, it has been found thatthe biaxially oriented thermoplastic coated kraft paper offers severaladvantages with respect to the construction of a multi-wall bag.Foremost, the biaxially oriented thermoplastic film layer has been foundto provide an improved printing surface as opposed to kraft papers whichhave been treated with a fluorochemical agent. The improved printingsurface is achieved, in part, by providing a smoother and non-abrasiveprinting surface. As a result, the printing surface requires less ink tobe applied while enhancing the sharpness and contrast of the appliedinks. Consequently, ink printing costs are lowered. The resultinggraphics are cleaner and crisper since the absorptive paper layer doesnot directly interact with or absorb the ink as occurs withfluorochemically treated papers.

[0030] Similar properties are also achieved when using the metal or foillayer embodiment. Again, an improved print quality is achieved while atthe same time using less ink. As set forth in Table 1A, paper coatedwith the metal or foil layer also exhibits excellent WVTR properties.

[0031] Additionally, the use of the coated paper as set forth in thevarious embodiments offers additional advantages in printing operations.To the extent different types of kraft papers may be used on consecutiveprinting runs, there is no longer a need to switch inks based upon thetype of paper. When various types of kraft paper are coated according tothe present invention, the resulting papers are all compatible with asingle type of ink and do not require time consuming and costly inkswitching at the printing stage.

[0032] Additionally, coated paper when used as an outer ply for amulti-wall bag results in the outer ply having improved strengthproperties and tear resistance compared to a similar bag made with anuncoated kraft paper. For instance, when a kraft paper, rated at aconventional 41 pounds, is coated as set forth above in reference toFIG. 3, the resulting coated paper has a rating of between about 70 toabout 80 pounds. Without the biaxially oriented film coating, a 41 poundkraft paper when treated with a traditional calendaring, clay coating,or metalizing process contributes only 15 to 20 pounds of strength underUniform Freight Classification ICC Rule 40. This additional strength, adirect result of the biaxially oriented film layer 44, allows a 25 poundbag of pet food which is conventionally shipped in a 4-ply bag to beshipped in a 3-ply bag. As a result, the material and shipping costs ofthe bag are decreased while achieving the attendant improvements notedabove with respect to improved graphics and printability.

[0033] The use of the coated paper in a multi-wall bag constructionpermits a converter kraft grade of interior ply layers to be used whilestill meeting the requirements of ICC Rule 40. Heretofore, compliancewith ICC Rule 40 effectively excluded the use of less expensiveconverter kraft grades in multi-wall bags in favor of the more expensiveand stronger natural kraft papers. The use of coated paper in bagconstruction allows interior ply layers to be made of converter kraftwhile still meeting the performance standards set forth in ICC Rule 40.

[0034] Tables 1A and 1B below set forth test data with respect tophysical properties and performance data of polypropylene coatedbleached kraft papers and metallized polypropylene coated natural kraftpapers, along with various control kraft and metallized kraft papers.With respect to the test results seen in Tables 1A and 1B, the paperweight was determined according to TAPPI official test method T-410.Porosity measurements were made according to TAPPI official test methodT-460. The tensile strength and tear resistance determination of thepaper were made using TAPPI test methods T-494 and T-414 respectively.The Dart Impact data was collected using ASTM 1709 methods. While notseparately set forth, the coated paper was noted to have excellentglueability properties with respect to paper-paper, paper-film, andfilm-paper adhesion.

[0035] As noted in Table 1A, the WVTR properties of the coated paper aresignificantly improved compared to WVTR values for conventional priorart outer ply construction. When incorporated into a multiple wall bag,the coated paper enhances the freshness of products sealed within thebag. In addition, decreasing vapor loss also provides for improved odorcontrol. The ability to provide for grain and animal food products in alow odor release bag can be important in retail environments where odorsmay be absorbed by clothing merchandise or be objectionable to near fooddispensing areas.

[0036] As further noted in Tables 1A and 1B, the properties of thecoated paper have the indicated values for tear and strength properties.As seen in reference to Table 1B, the single sheet and samples 1 through3 have a core fiber basis weight of about 50. Following coating with thebiaxially oriented polypropylene film, the basis weight and strengthincreases as indicated in Table 1B when compared to the comparison 1natural kraft 50-pound basis weight paper and the comparison 2 43-poundbasis weight metallized prior art paper. As provided for in Table 2, theoverall improvements in bag strength which result from use of the coatedpaper on an exterior ply may be seen in comparison to control bagswithout the coated paper enhancement. TABLE 1A MET PP/Extruded/ METPP/Extruded/ Test Description PP/Extruded/BL NK NK NK Basis Weight70.715 72.738 68.0 (Llbs/3000 ft²) Porosity Avg.: Exceeds 1800 Exceeds1800 Exceeds 1800 (Sec/100 cc Air) Std. seconds seconds seconds TAPPIT460 Dev.: Low: High: 20° Gloss Avg.: 34.3 0 @ 20° and 60° 0 @ 20° and60° (Degrees) Std. 1.83 Geometry Geometry TAPPI T480 Dev.: Low: 31.8High: 36.9 MD CD MD CD MD CD Tensile Avg.: 36.38 19.22 49.51 22.65 46 28(Lbf/in) Std. 1.74 1.38 3.10 1.96 TAPPI T494 Dev.: Low: 33.37 17.0546.42 19.40 High: 37.60 20.55 53.65 24.65 TEA Avg.: 4.02 53.20 7.8126.05 7.3 24 (Ftlbs/ft²) Std. 0.39 16.26 1.55 4.85 TAPPI T494 Dev.: Low:3.39 25.48 6.51 21.38 High: 4.44 66.60 9.73 33.21 Tear Avg.: 159.6 148.5125.5 187.7 137 134 (Grams) Std. 9.6 8.3 11.6 3.2 TAPPI T414 Dev.: Low:148.0 141.4 114.5 182.7 High: 174.6 161.0 142.3 191.6 WVTR 0.48 0.010.01 (g/100 in²/24 hrs @ 100° F. and 90° RH) ASTM E-96-80

[0037] TABLE 18 Basis Weight (before/after coating) Test Param TestDiscripto Test Test Units Impact Dart Drop Impact Ft.-lb force Std DevMullen A NA Mullen A Avg lbs/sq in Mullen A Std Deviat lbs/sq in Tear MDTear Avg gms Tear Std Deviation gms CD Tear Avg gms Tear Std Deviationgms Tensile MD Tens Energy Abs Av Ft-lb/sq ft Tens Energy Abs StFt-lb/sq ft Tens Ext Stif Avg lbs/inch Tens Ext Stif Std De lbs/inchTens Stretch Avg Percent Tens Stretch Std De Percent Tensile Avglbs/inch Tensile Std Deviatio lbs/inch CD Tens Energy Abs Av Ft-lb/sq ftTens Energy Abs St Ft-lb/sq ft Tens Ext Stiff Avg lbs/inch Tens Ext StifStd De lbs/inch Tens Stretch Avg Percent Tens Stretch Std De PercentTensile Avg lbs/inch Tensile Std Deviatio lbs/inch WVTR Single SheetComparison ONTIC Metal COMPARISON 2 Single Sheet COMPARISON 1 Sample 1Vac Met ONTIC White NK METAL Sample 2 Sample 3 C1S/Metallized 50/70 5050/72 50/72 50/72 43 Test Methods ASTM 1709 0.2045 0.6547 0.029 0.165101 46 79 67 32 14 2 16 7 4 TAPPI 159.6 133.1 125.5 137.68 136.18 49.6T-414 om-88 9.6 11.6 6.53 5.05 1.03 148.5 125.7 187.7 138.14 131.6246.98 8.3 3.2 3.77 4.56 1.92 TAPPI 4.02 7.81 4.69 2.2 T-494 om-88 0.391.55 0.64 0.78 3940 2770 221 115 6.51 1.6 1.29 9.73 0.16 0.26 36.3849.51 39.2 22.5 1.74 3.1 1.4 3 53.2 26.05 19.4 4.51 16.26 4.85 1.05 1.241870 1250 129 65 21.38 6.5 3.79 33.21 0.27 0.81 19.22 22.65 32.1 13.31.38 1.96 1 1.2 ASTM F-372

[0038] The coated paper is useful for single-wall bags, multi-ply bags,or stand-up pouches in which the outermost ply is of a coated paper asdescribed herein. The resulting bag has advantages in terms of themechanical packaging capabilities of the bag. The exterior, i.e.,printed surface of the bag/paper has an extremely smooth and glossytexture. Suction belts and cups used on mechanical packaging equipmentare able to better grasp the bag. The improved gripping results in bagprocessing in which the outer face is not torn or damaged by the use ofoverly aggressive handling techniques or application of excessive vacuumpressure to the handling equipment.

[0039] The improved bag strength which results from inclusion of thecoated paper in the bag construction significantly increases the tearresistance of the bag. Consumers will often grab a bag along an upperseam or gusset wall. The coated paper provides sufficient tearresistance to the bag that the integrity of the bag is maintained duringhandling along key stress points. This additional strength alsofacilitates the incorporation of handles into the bag, such handlesbeing known in the art.

[0040] Further, bags made with the biaxially oriented film-coated paperare more resistant to punctures, tears, and abrasion of the exteriorlayer. The exterior layer comprises the print surface upon whichpackaging graphics are printed. As a result, the improved strength andtear resistance maintains the shelf appeal of the packaging. Consumersperceive visible tears or abrasions in bag packaging as an indication ofunderlying weakness of the bag and/or a compromise of the product'sintegrity. By reducing the incidence of tears and abrasions in the bagexterior, retailers do not have to discount or remove as much product asa result of damaged packaging.

[0041] An additional benefit of providing a multi-wall bag having theouter ply of the coated paper described herein is that the resultingbags have shown improved resistance to external moisture damage.Heretofore, conventional pet food bags and similar products had anexterior ply layer which offered poor resistance to moisture. As aconsequence, exposure of the bag to rain or moisture would greatlyweaken the bag strength. Further, visible moisture damage lessened theattractiveness of the bag graphics and was frequently perceived by theconsumers as indicative of potentially spoiled or damaged goods. The useof the coated paper, described herein as the exterior ply layer,substantially increases the resistance of the bag to moisture. Thisresistance has positive effects on the bag strength as well as theappearance of the bag graphics.

[0042] The biaxially oriented coated paper described herein provides amore stable outer ply for use in a multi-wall converting process. Notonly will the coated paper allow use of fewer plies, or alternativelythe use of lower basis weight paper for intermediate plies, thereduction in ply numbers and/or basis weight has advantages in the bagmanufacturing process. The increased stability of the outer ply allowshigher bag machine and tuber speeds to be utilized, increasing theefficiency of the bag-making operation.

[0043] Additionally, the coated paper of the present invention maintainsstability during the converting process. For instance, usingconventional exterior ply paper, the conventional outer ply becomes verybrittle and difficult to convert following printing of the outer ply.The increased brittleness is brought about by water loss occurringduring the printing/lamination process. In comparison, the biaxiallyoriented coated paper of the present invention exhibits minimal moistureloss during converting and printing steps. As such, the outer plymaterial is easier to handle and any associated natural kraft orbleached base paper in the interior plies is likewise maintained in agood condition.

[0044] During printing production steps, the biaxially oriented coatedpaper exhibits improvements in manufacturing efficiencies. A significanttime factor of printing on prior art paper involves the drying of thepaper following application of one or more ink colors. Using thebiaxially oriented coated paper reduces the ink volume by a factor oftwo to three without loss of color intensity or hues. Since printingoccurs directly on the film side of the paper, there is no to minimalabsorption of the ink which reduces drying requirements, uses less ink,and helps maintain favorable moisture conditions by minimizing use ofdrying ovens. As a result, the graphics printing can be done at a higherrate of speed and using less inks than on a conventional outer ply paperof conventional design.

[0045] The outer ply layer heretofore used within the bag industryexhibits a tendency to crack when folded during a bag-making operation.As a result, the gussets and bottom folds often exhibit a poorappearance and undesirable shelf appeal. Additionally, the crack impairswhatever barrier properties may have been present within theconventional outer ply layer. The present invention's use of a biaxiallyoriented polypropylene or polyester has been found to greatly increasethe flex characteristics of the paper. As a result, folds and creasesare additionally protected from cracking and thereby increase both theappearance as well as the barrier properties of the resulting multi-wallbags.

[0046] Additionally, the biaxially oriented films of the coated paperdescribed herein will readily receive an extruded or film applied heatseal coating such as a low density polyethylene. As such, the coatedpaper of the present invention becomes an ideal substrate for stand-uppouches and other containers where heat sealing may be used to seal thecontainer. As previously noted, the coated paper of the presentinvention also exhibits excellent properties with respect toglueability.

[0047] Additionally, sealed multi-wall bags in which the exterior plycomprises the coated paper of the present invention have demonstratedimproved properties with respect to control bags in standard drop tests.Set forth in Table 2 is comparative data between a conventional 4-plymetallized bag (37.5 lb. capacity) having a fluorchemical outer plytreatment in comparison to a similar multi-ply bag having the outermostply of a coated paper using the metallized biaxially oriented film(ONTICTM) as described herein. TABLE 2 BAG COMPARISON Bag: 75 OPP/2-60NK/Outer Ply Outer Ply Old: 43 C1S/Metallized Outer Ply New: ONTIC MetalOLD NEW Test Test 4-PLY 4-PLY Parameter Test Test Units BAG BAG Mullen ANA Mullen A Avg lbs/sq in 143 215 (bursting) D774M-97 Mullen A Std Dev.lbs/sq in 9 12 Tear MD Tear Avg gms 127.3 173.26 Tear Std Deviation gms6.08 8.92 CD Tear Avg gms 119.04 138.78 Tear Std Deviation gms 4.39 8.77Tensile MD Tens Energy Abs Avg Ft-lb/sq ft 13.4 13.5 Tens Energy Abs StdFt-lbs/sq ft 1.83 1.09 Dev. Tens Ext Stif Avg lbs/inch 10000 10500 TensExt Stif Std Dev. lbs/inch 273 411 Tens Stretch Avg Percent 1.55 1.39Tens Stretch Std Dev. Percent 0.17 0.18 Tensile Avg lbs/inch 96.6 102.5Tensile Std Deviation lbs/inch 6.8 11.5 CD Tens Energy Abs Avg Ft-lb/sqft 34.8 53.8 Tens Energy Abs Std Ft-lb/sq ft 0.75 9.07 Dev. Tens ExtStif Avg lbs/inch 4190 5950 Tens Ext Stif Std lbs/inch 201 233 DeviationTens Stretch Avg Percent 3.82 3.44 Tens Stretch Std Percent 0.43 0.35Deviation T nsile Avg lbs/inch 57.2 72.4 Tensile Std Deviation lbs/inch2.9 2.8

[0048] Multi-wall bags made according to the exemplary embodimentsdescribed above exhibit excellent resistance to grease migration throughthe packaging. Grease barriers are important with respect to packagedanimal feed including dog food or cat food. It has been found thatmulti-wall bags as referenced in Table 2 using the biaxially coatedpaper will provide a grease barrier for 30 days when tested usingrefined poultry fat maintained in the bags at temperatures of 120° F.

[0049] The improvements in overall bag strength brought about byincorporation of the biaxially oriented film-coated paper results in abag packaging having three times the resistance to impact damagecompared to a conventional bag of 50 lb. natural kraft paper. As aresult, it is possible to eliminate one or more plies from a multi-plybag when the exterior bag layer is comprised of the biaxially coatedpaper described herein. As a result, packaging bags can be providedwhich are stronger than comparative bags, use less material, offerimproved print and graphic capabilities, have improved resistance toabrasion and tearing of the bag exterior surface, and offer improvementsin terms of water vapor transmission properties, water resistanceproperties, and grease barrier properties. Such improvements, dependingupon the bag size and contents, may permit a single-wall bag or stand-uppouch of superior performance to be constructed using biaxially orientedfilm coated paper. As noted in Table 2, the burst strength (Mullen A) ofthe bag is improved by about 33% in comparison to an identical baghaving an uncoated outer ply.

[0050] The ability to vary the dimensions of width, gusset size, andtube length allow one to provide for a multi-ply bag having a lowercenter of gravity and using the same materials as similar volume bagsbut having a higher center of gravity. The lower center of gravityplaces greater stress upon certain seams used to form the bag. Theinclusion of the coated paper as the outermost ply provides sufficientbag strength that variations in bag dimensions may be readily madewithout having to change the underlying materials used to form thevarious ply layers.

[0051] While many of the above referenced embodiments discuss the use ofextrusion to apply various layers to the coated paper, it is understoodby one having ordinary skill in the art that one or more of the appliedlayers coating the paper may be provided by the application of films.The use of films to provide layers within a coated paper or boardstructure is well known within the art.

[0052] Although preferred embodiments of the invention have beendescribed using specific terms, devices, and methods, such descriptionis for illustrative purposes only. The words used are words ofdescription rather than of limitation. It is to be understood thatchanges and variations may be made by those of ordinary skill in the artwithout departing from the spirit or the scope of the present invention,which is set forth in the following claims. In addition, it should beunderstood that aspects of the various embodiments may be interchanged,both in whole or in part. Therefore, the spirit and scope of theappended claims should not be limited to the description of thepreferred versions contained therein.

That which is claimed is:
 1. A multiple-ply bag comprising: a tubularmulti-wall structure having upper and lower ends, the upper and lowerends being sealable; front and back walls joined at opposite bag sidesby at least two side gussets running the length of the bag; and, anouter ply layer of said multi-wall bag having a base layer of a kraftpaper, a layer of polyethylene applied to an exterior side of said kraftlayer, and, an outermost layer of a biaxially oriented thermoplasticpolymer applied to the polyethylene layer, said outermost layer furtherdefining a printable surface. 2 An improvement in a multi-wall baghaving at least an inner ply and an outer ply, said improvementcomprising said outermost ply having a fiber layer of an about 40 to anabout 60 pound basis weight paper, an exterior side of the paper havingabout a 5 to about a 15 pound layer of polyethylene applied to saidpaper, said polyethylene layer being in further contact with anoutermost layer of an oriented thermoplastic polymer selected from thegroup consisting of a polypropylene, a polyester, or a combinationthereof.
 3. A multiple-ply bag comprising: a multi-wall structure havingat least two ply layers, said multi-wall structure further having upperand lower ends being sealable; front and back walls joined at oppositeback sides by at least gussets running a length of the bag; an exteriorply of said at least two ply layers comprising a paper substrate; anextrusion coating of polyethylene on a first side of said papersubstrate; and, a film layer applied to said polyethylene coating, saidfilm layer defining a non-absorptive printing surface which is selectedfrom the group consisting of biaxially oriented polypropylene films,biaxially oriented polyethylene films, metallized films of biaxiallyoriented polypropylene, and metallized films of biaxially orientedpolyester.
 4. A multiple-ply bag comprising: an inner ply layercomprising a paper having a laminated surface, the laminated surfacedefining an innermost surface of the multiple-ply bag; a second plylayer of an uncoated paper adjacent an uncoated surface of said innerply; a third ply layer of an uncoated paper positioned between saidsecond ply layer and a fourth ply layer, said fourth ply layer definingan exterior ply of said multi-ply bag, said fourth ply layer furtherdefining a coating of a 5 to 15 lb. weight/3000 sq. ft. of polyethyleneand a film layer applied to a surface of said polyethylene, said filmlayer comprising a biaxially oriented film selected from the groupconsisting of a biaxially oriented polypropylene film, a biaxiallyoriented polyethylene film, a metallized film of biaxially orientedpolypropylene, and a metallized film of biaxially oriented polyester;wherein said multiple-ply bag has increased burst resistance andimproved tear strength than a comparable four-ply bag without said filmlayer.
 5. The multiple-ply bag according to claim 4 wherein said fourthply layer comprises a paper having a fiber content of about a 35 toabout a 90 lb. basis weight.
 6. The multiple-ply bag according to claim4 wherein said fourth ply has a film layer selected from the groupconsisting of metallized films of biaxially oriented polypropylene andmetallized films of biaxially oriented polyester, said multiple-ply bagfurther having a WVTR of about 0.01 g/100 in.²/24 hrs. or less.
 7. Themultiple-ply bag according to claim 4 wherein at least one of saidsecond and said third ply layers is provided by a converter kraft paper.8. The multiple-ply bag according to claim 4 wherein said second ply andsaid third ply are provided by a converter kraft paper.